1. Field of the Invention
The present invention relates to a modular sensor for damage detection, manufacturing method, and structural composite material.
2. Description of the Related Art
Conventionally, fiber reinforced resin composite material (hereinafter called “composite material”) which is light and high in strength has been applied to various structural composite materials such as aircraft structures, space equipments, high-rise buildings, public infrastructures, high-speed vehicles, and the like. Since behavior of damage progress of the composite material is unclear compared to that of metal material, “safe life design” has been adopted in case of structuring structural composite material. However, when this design method is adopted, weight of structure becomes heavy, and properties of the composite material (light and high in strength) cannot be taken in advantage fully.
Therefore, in these days, development in technique to detect damage of the composite material is on progress to achieve “damage tolerance design”, that can take the properties of the composite material in advantage fully. For example, a technique to embed film-shaped piezo elements and cables sandwiched between polyimide films into the composite material, to detect outputs from the piezo elements which are produced based on vibration applied to the structure, and to detect damage of the composite material based on detected waveforms, has been disclosed (for example, see Patent Document 1: U.S. Pat. No. 6,370,964).
However, since a place where polyimide film used in the technique is embedded is limited, it is difficult to detect damage with high degree of accuracy by embedding the polyimide film where damage occurs frequently. Therefore, recently proposed is to embed an optical fiber provided with FBG (Fiber Bragg Grating) sensor into the composite material, and proposed is a damage detection system to detect damage of the composite material with high degree of accuracy, according to a reflected light property detected by the FBG sensor.
Meanwhile, the optical fiber used in aforementioned damage detection system has a typical wire diameter of 125 μm to 150 μm, which would be approximately same size with a thickness of one prepreg layer constructing the composite material (125 μm to 200 μm). Therefore, the property of the composite material may be decreased. In order to solve this problem, a “thin diameter” optical fiber whose wire diameter is less than or equal to half the thickness of one prepreg layer (approximately 52 μm) has been developed recently.
However, since the thin diameter optical fiber is so thin that managing with the optical fiber is difficult and visibility is disturbed, a problem arose in that it is difficult to embed the optical fiber with thin diameter into the composite material.